1. Field of the Invention
The invention in general relates to steam turbine control systems having an auto/manual operator's panel and more particularly to pushbutton operation of the manual section.
2. Description of the Prior Art
In the field of steam turbine control, many systems exist which utilize a primary controller in the form of a programmable digital computer as well as a redundant or backup computer. The computer's capability to monitor, memorize, calculate, test and make instant decisions results in a control system which is faster, more accurate and far superior to purely mechanical or analog control systems.
An improved digital control system for a steam turbine has been developed which includes primary and redundant base controllers as well as interconnected and coordinated functional modules each having its own microcomputer to execute specific functions. That is, the control system structure is based upon distributed processing, with this modular architecture providing for greater flexibility and minimizing risk of control loss and total system shutdown due to any single failure. The system can be serviced while on-line without the necessity for shutting down the turbine's operation and servicing of the apparatus can be accomplished in a minimal amount of time. One example of such distributed processing turbine control system is described and claimed in U.S. Pat. No. 4,368,520 assigned to the assignee of the present invention and hereby incorporated by reference.
The control system of the referenced patent includes a plurality of valve position control circuits for controlling the steam admission valves, with each circuit including its own programmable digital computer in two-way digital communication with a base controller from which it receives signals relative to the individual valve control. The valve position control circuits are selectively addressable to receive a particular valve related signal from the controller to in turn generate an individual valve drive signal for the valve it is controlling. The system is operable both in an automatic and a manual mode and when in the manual mode all of the valve position control circuits function to receive operator-entered command signals.
The operator-entered command signals are generated by activation of certain pushbuttons on the manual section of an operator's panel. For example, the operator may want to change the turbine speed (or load) by moving the steam admission valves and depression of the appropriate pushbutton will effect the necessary movement.
If for some reason the activated pushbutton sticks, after removal of the operator's finger pressure, the valves will objectionally continue to move. The present invention provides for contingency operation in such stuck pushbutton situation.